Photoelectric conversion device and fabrication method therefor

ABSTRACT

A photoelectric conversion device comprises a high-refractive-index portion at a position close to a photoelectric conversion element therein. And, the high-refractive-index portion has first and second horizontal cross-section surfaces. The first cross-section surface is at a position closer to the photoelectric conversion element rather than the second cross-section surface, and is larger than an area of the second cross-section surface, so as to guide an incident light into the photoelectric conversion element without reflection.

CROSS REFERENCE TO RELATED APPLICATION

This application is division of application Ser. No. 13/974,379 filedAug. 23, 2013, which is a continuation of U.S. application Ser. No.13/190,921 (now U.S. Pat. No. 8,546,173), which is a division of Ser.No. 12/065,301 (now U.S. Pat. No. 8,013,409), which is a 371 ofinternational PCT/JP2006/319226 filed Sep. 21, 2006. The entiredisclosures of these earlier applications are hereby incorporated hereinby reference.

TECHNICAL FIELD

The present invention relates to a photoelectric conversion device and afabrication method therefor, and particularly to a condensing portion ofthe photoelectric conversion device.

BACKGROUND ART

In the case of a photoelectric conversion device used for a digitalcamera and camcorder, a pixel is miniaturized through decrease of thedevice in size and change of the device to multiple pixels. Inconnection with miniaturization of the pixel, the area of the lightreceiving portion of the photoelectric conversion element is decreasedand incident light quantity is decreased, thereby the sensitivity isdeteriorated.

To improve deterioration of the sensitivity, deterioration of thesensitivity is reduced by forming an on-chip microlens on the lightreceiving portion of the photoelectric conversion device and condensinglight to the light receiving portion. Moreover, in recent years, aconfiguration is known in which an optical waveguide for condensinglight by using light reflection is formed between an on-chip microlensand a photoelectric conversion element.

A method for fabricating an optical waveguide of the above photoelectricconversion device has a step of filling a well-shaped portion after astep of forming a well-shaped portion on an insulating layer in general.A material for embedding uses a material having a high refractive indexcompared to that of the insulating layer. Then, light is reflected frominterfaces due to the refractive index difference between the insulatinglayer and the high refractive index portion and condensed.

However, as pixels are further miniaturized, the aspect ratio of awell-shaped portion becomes high and a void may be produced in thewell-shaped portion in an embedding step. Particularly, this problemeasily occurs in a CMOS image sensor having multilayer wiring.

Therefore, there is the following technique to solve the problem in theembedding step. Japanese Patent Application Laid-Open No. 2004-193500discloses a method for forming an optical waveguide by dividing it intoa plurality of layers having different diameters.

By forming an optical waveguide constituted of a plurality of layers foreach layer, it is possible to preferably fill a high refractive indexportion without producing a void. Specifically, by repeating a step offilling the inside of a well-shaped portion after a step of forming awell-shaped portion, an optical waveguide free from void is formed.

Moreover, in the case of a structure having a plurality of opticalwaveguides, the diameter of an optical waveguide at the light incomingside. Thereby, filling of the inside and introduction of light are madeeasy.

Furthermore, in Japanese Patent Application Laid-Open No. 2000-150845,it is described to form an etching stop film in order to make the depthof a well-shaped structure constant when forming a well-shaped portion.

Furthermore, Japanese Patent Application Laid-Open No. 2002-359363discloses a structure having a light guide layer in a CCD-typephotoelectric conversion device. That is, a light transmission film isformed and then, the side wall of the light transmission film issurrounded by a reflection film. The shape of the light transmissionfilm is tapered toward a light receiving portion.

However, in the case of a structure having a plurality of opticalwaveguides, when light is reflected at an upper-layer optical waveguideand enters a lower-layer optical waveguide, a case of not satisfying areflection condition occurs. Then, the light not entering thephotoelectric conversion element becomes color mixture or noisecomponent.

Moreover, when bringing a lower-layer optical waveguide into a verticalshape in a structure having a plurality of optical waveguides, light notsatisfying a reflection condition depending on an incident angle may bepresent even for the light not reflecting from the interface of anupper-layer optical waveguide but directly entering the interface of alower-layer optical waveguide.

Moreover, in the case of a light guide layer of a CCD-type photoelectricconversion device described in Japanese Patent Application Laid-Open No.2002-359363, incident light quantity may be decreased because the areaat the light incoming side of a light transmission film is decreased.Furthermore, light may be reflected by the light shielding film of atransfer electrode instead of entering a photoelectric conversionelement.

DISCLOSURE OF THE INVENTION

A photoelectric conversion device comprises:

a semiconductor substrate;

a photoelectric conversion element arranged in the semiconductorsubstrate;

a plurality of MOS transistors each having a gate electrode for readingelectric charge from the photoelectric conversion element;

a plurality of insulating layers arranged at a position higher than thegate electrode;

a multilayer structure having patterned layers arranged at a portionhigher than the gate electrode; and

a plurality of high-refractive-index portions each having refractiveindex higher than that of the insulating layer so as to guide light intothe photoelectric conversion element by the reflection at an interfacebetween the insulating layer and the high-refractive-index portion.

The high-refractive-index portion at a position closest to thephotoelectric conversion element among the high-refractive-indexportions has,

a first cross-section surface and a second cross-section surfacehorizontal to a light receiving surface of the photoelectric conversionelement at a position closer to the photoelectric conversion elementrather than the patterned layer at a position closest to thephotoelectric conversion element among the patterned layers, and

the area of the first cross-section surface at a position closer to thephotoelectric conversion element rather than the second cross-sectionsurface is larger than the area of the second cross-section surface.

Other features and advantages of the present invention will be apparentfrom the following description taken in conjunction with theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a photoelectric conversion device of firstembodiment;

FIG. 2A is a sectional view of the photoelectric conversion device ofthe first embodiment of the present invention;

FIG. 2B is a sectional projection view of an optical waveguide of thephotoelectric conversion device of the first embodiment of the presentinvention;

FIG. 3A is a sectional view of a part of an optical waveguide;

FIG. 3B is a sectional view of a part of an optical waveguide;

FIG. 4 is a sectional view of a photoelectric conversion device ofsecond embodiment;

FIG. 5A is a sectional view of a photoelectric conversion device ofsecond embodiment;

FIG. 5B is a sectional projection view of an optical waveguide of thephotoelectric conversion device of the second embodiment;

FIG. 6 is an illustration showing a relation between a film thicknessand a dark current;

FIG. 7 is a sectional view of a photoelectric conversion device of thirdembodiment;

FIG. 8A is a fabrication flow of the third embodiment;

FIG. 8B is a fabrication flow of the third embodiment;

FIG. 8C is a fabrication flow of the third embodiment;

FIG. 9D is a fabrication flow of the third embodiment;

FIG. 9E is a fabrication flow of the third embodiment;

FIG. 9F is a fabrication flow of the third embodiment;

FIG. 10G is a fabrication flow of the third embodiment;

FIG. 10H is a fabrication flow of the third embodiment;

FIG. 10I is a fabrication flow of the third embodiment;

FIG. 11 is a sectional view of a photoelectric conversion device offourth embodiment;

FIG. 12 is a sectional view of a photoelectric conversion device offifth embodiment;

FIG. 13 is a block diagram of an image pickup module to which aphotoelectric conversion device of the present invention is applied;

FIG. 14 is a block diagram showing a configuration of a digital cameraserving as an image pickup system; and

FIG. 15 is an equivalent circuit of pixels of a photoelectric conversiondevice of the present invention.

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention and,together with the description, serve to explain the principles of theinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

In the case of a photoelectric conversion device of the presentinvention, a plurality of stacked optical waveguides using therefractive index difference of the interface between an insulating layerand high refractive index portion having a refractive index higher thanthat of the insulating layer are formed. The high refractive indexportion has at least a first high refractive index portion formed at aposition closest to the photoelectric conversion element and a secondhigh refractive index portion formed above the first high refractiveindex portion. The first high refractive index portion is formed at aposition closer to the photoelectric conversion element than a patternedlayer formed at a position closest to the photoelectric conversionelement. Moreover, in the first high refractive index portion, the areaon a face closer to the photoelectric conversion element is larger thanthe area of a face horizontal to the light receiving surface of thephotoelectric conversion element.

In this case, the high refractive index portion is formed on asemiconductor substrate correspondingly to the photoelectric conversionelement and the area and the element have a refractive index higher thanthat of an insulating layer constituting an optical waveguide.Specifically, they are formed of silicon nitride or oxynitridingsilicon. Moreover, the insulting layer is formed of a material having arefractive index lower than that of the layer. For example, the layer isformed of silicon oxide. Moreover, the high-refractive-index layer showsa layer for forming a high refractive index portion.

By forming the shape of a high refractive index portion closest to aphotoelectric conversion element into the shape of the presentinvention, the area becomes a configuration for easily satisfying thereflection condition of an optical waveguide and it makes possible toeffectively bring light into the photoelectric conversion element.

By setting the first high refractive index portion having the shape ofthe present invention to a position closer to the photoelectricconversion element than a patterned layer formed on a position closestto the photoelectric conversion element, the design versatility of thepatterned layer is improved. It is possible to narrow the intervalbetween patterns in accordance with miniaturization of pixels. Moreover,in the case of a photoelectric conversion device having a plurality ofpatterned layers, by forming a second high refractive index portion, itis possible to make oblique ray enter the photoelectric conversionelement. Therefore, it is possible to narrow the interval betweenpatterned layers to be arranged at a position closet to thephotoelectric conversion element without deteriorating condensingefficiency of the photoelectric conversion element.

In this case, the patterned layer is a wiring layer or light shieldinglayer and is constituted of a conductive material such as aluminum orcopper. Moreover, a gate electrode made of polysilicon is excluded. Itis allowed that a patterned layer formed at a position closest to aphotoelectric conversion element is a patterned layer for specifying theopening of the photoelectric conversion element. The pattern forspecifying the opening of the photoelectric conversion element is usedto decide the margin of a region entering the photoelectric conversionelement. In this case, a pattern which decides the opening is known byperforming optical simulation of an element cross section.

Moreover, it is recommended to form the second high refractive indexportion to be formed above the first high refractive index portion tothe following shape. That is, the area of the second plane at thephotoelectric conversion element is decreased compared to the firstcross-section surface in which the second high refractive index portionis present. Even if a patterned layer formed at a position closest tothe photoelectric conversion element specifies the opening, it ispossible to effectively condense light by increasing the effectiveopening area of the photoelectric conversion element while narrowing theinterval between patterns of the patterned layer. Particularly, this isvery effective when setting an optical waveguide constituted of the highrefractive index portion of the shape to the highest position.

Moreover, it is recommended to make the size of the surface area of thephotoelectric conversion element of a high refractive index portionformed at a position closest to a photoelectric conversion elementsmaller than the surface area of the photoelectric conversion element.In this case, it is possible to decrease the leak of light to portionsother than the photoelectric conversion element and this is particularlyeffective when considering a shift during fabrication.

It is a matter of course that the position of an optical waveguide orthe number of optical waveguides is properly optimally designed.

For example, it is preferable that the high refractive index portion hasa thickness between 200 and 2,000 nm in the film thickness direction.More preferably, the area has a thickness of 500 nm or more. It ispossible to decrease the damage on a photoelectric conversion element byvirtue of the high refractive index portion when there is an etchingstep after forming the area.

Moreover, it is allowed that the high refractive index portion also hasthe function of an etching stop layer. Furthermore, since the area hasthe thickness of this range, it is possible to effectively use thefunction of an optical waveguide using reflection on the interfacebetween the high refractive index portion and the insulating layer. Thisis described below.

In this case, FIG. 6 shows the relation between the distance from thelight receiving surface of a photoelectric conversion element to thebottom of a well-shaped portion and dark current when applyingwell-shaped portion to a photoelectric conversion device. Thiswell-shaped portion forms in the insulating layer formed at a positionclosest to a photoelectric conversion element by plasma etching. In thiscase, the photoelectric conversion device uses a photoelectricconversion device after forming a well-shaped portion before forming ahigh refractive index portion. Moreover, the dark current is shown by arelative ratio by assuming a current which does not form a well-shapedportion as 1.

From this graph, it is found that dark current increases as the distancefrom the light receiving surface of a photoelectric conversion elementto the bottom of the well-shaped portion is decreased. And the darkcurrent is decreased at 500 nm or more. Therefore, it is possible todecrease the number of damage at the time of plasma etching when thethickness of a high refractive index portion formed on a photoelectricconversion element is 500 nm or more.

Moreover, an LDD (Lightly Doped Drain) structure may be used for afield-effect transistor included in a photoelectric conversion device toreduce dark current by electric field concentration nearby a draindiffusion region. In the case of the LDD structure, a side wall isformed on the gate electrode of the transistor (not illustrated).

When the LDD structure is used, it is possible to form a side wall byusing the high-refractive-index layer for forming the previous highrefractive index portion. As a specific step, after forming the gateelectrode of a transistor, a high-refractive-index layer is formed bycovering the gate electrode. Then, by anisotropically etching thehigh-refractive-index layer, it is possible to form a high refractiveindex portion and side wall at the same time. Moreover, by forming themin this step, it is possible to decrease man-hours and protect aphotoelectric conversion element from the etching when forming a sidewall. It is a matter of course that even when performing etchings inseparate steps, it is possible to decrease the number of man hoursbecause of using the same high-refractive-index layer.

In this case, when increasing the thickness of the high-refractive-indexlayer for protection from etching damages, it may be impossible to forma side wall through etching. Also, it may be impossible to form itbecause the thickness of the layer is insufficient even when decreasingthe side wall in thickness. The preferable thickness is the thicknessequivalent to the thickness of a gate electrode, for example, 200 nm.From FIG. 6, it is found that the number of damage on a photoelectricconversion element in an etching step can be decreased even in thisthickness.

In the case of any structure, it is possible to effectively use thefunction of an optical waveguide using the reflection on the interfacebetween the high refractive index portion having the thickness and theinsulating layer.

Hereafter, the “cross-section surface” of a high refractive indexportion shows a cross section in the direction horizontal to the lightreceiving surface of the photoelectric conversion element of the highrefractive index portion. Moreover, it is assumed that a certain planeof a high refractive index portion is a first cross-section surface anda plane closer to the photoelectric conversion element than the firstcross-section surface is a second plane.

In this case, the “on semiconductor substrate” shows “on the mainsurface of a semiconductor substrate” on which pixels are formed.Moreover, it is assumed that the direction from the main surface of thesemiconductor substrate to the inside of the substrate is downwarddirection and the reverse direction is upward direction.

Furthermore, a semiconductor substrate serving as a material substrateis shown as “substrate”. However, the following case in which thematerial substrate is treated is also included. For example, a member onwhich one or more semiconductor regions are formed, member present atthe middle of a series of fabrication steps or member passing through aseries of fabrication steps can be referred to as a substrate.

(Circuit Configuration of Pixel)

FIG. 15 shows a circuit configuration of pixels in a CMOS-typephotoelectric conversion device which is a type of a photoelectricconversion device. Pixels are shown by 1310.

The pixel 1310 is constituted by including a photodiode 1300 serving asa photoelectric conversion element, transfer transistor 1301, resettransistor 1302, amplifying transistor 1303 and selection transistor1304. In this case, a power supply line is shown by Vcc and an outputline is shown by 1305.

In the photodiode 1300, the anode is connected to a ground line and thecathode is connected to the source of the transfer transistor 1301.Moreover, the source of the transfer transistor can also serve as thecathode of the photodiode.

The drain of the transfer transistor 1301 constitutes floating diffusion(hereafter referred to as FD) serving as a transfer region, and the gateof it is connected to a transfer signal line. In the reset transistor1302, the drain is connected to the power supply line Vcc, the sourceconstitutes the FD and the gate is connected to a reset signal line.

In the amplifying transistor 1303, the drain is connected to the powersupply line Vcc, the source is connected to the drain of the selectiontransistor 1304 and the gate is connected to the FD. In the selectiontransistor 1304, the drain is connected to the source of the amplifyingtransistor 1303, the source is connected to the output line 1305 and thegate is connected to a vertical selection line to be driven by avertical selection circuit (not illustrated).

The circuit configuration shown above can be applied to all embodimentsof the present invention. For example, the circuit configuration can beapplied to a circuit configuration having no transfer transistor orother circuit configuration sharing a transistor by a plurality ofpixels. Moreover, a photoelectric conversion element can be applied tonot only a photodiode but also a phototransistor.

Embodiments of the present invention are described in detail byreferring to the accompanying drawings.

First Embodiment

FIG. 1 shows a sectional schematic view of the photoelectric conversiondevice of this embodiment in the direction vertical to a semiconductorsubstrate. FIG. 1 shows one pixel of the previously described CMOS-typephotoelectric conversion device. In the case of an actual photoelectricconversion device, a plurality of pixels like the above pixel are formedon a semiconductor substrate.

In the case of this embodiment, an optical waveguide structureconstituted of two optical waveguides is formed on one pixel of aphotoelectric conversion device. In this case, the second cross-sectionsurface of a first high refractive index portion 3 constituting anoptical waveguide nearby a photoelectric conversion element 2 is formedat a size larger than the area of a first cross-section surface.

FIG. 1 is described below in detail.

The first high refractive index portion 3 is formed on a semiconductorsubstrate 1 and covered with an insulating layer 4. Moreover, a firstpattern 5 and insulating layer 6 for covering the first pattern 5 areformed on the insulating layer 4 and a second pattern 7 is formed on theinsulating layer 6.

A second high refractive index portion 8 is formed above the first highrefractive index portion 3. Then, a planarized layer 9, color filterlayer 10, planarized layer 11 and on-chip microlens 12 formed on theplanarized layer 11 are provided above the second high refractive indexportion 8.

The first high refractive index portion 3 is formed on the photoelectricconversion element 2. The first high refractive index portion 3 is madeof a transparent material passing light and has a refractive indexhigher than the insulating layer 4 present around the area 3. It ispreferable to use a plasma SiN film, plasma SiON film, resist ortitanium oxide as the material of the first high refractive indexportion 3 satisfying the above condition. Moreover, the second plane ofthe first high refractive index portion 3 has a tapered shape having anarea larger than the first cross-section surface.

It is preferable that the first high refractive index portion 3 has athickness of 500 nm or more as previously described. Moreover, it ispreferable that the upper limit of the thickness is equal to the bottomside or the upper plane of the first pattern 5. Specifically, the upperlimit is approx. 2,000 nm. This is because the first pattern 5 is easilyformed like the case to the planarization step. It is possible todecrease the damage on photoelectric conversion element due to etchingwhen forming the second high refractive index portion 8 shown in FIG. 1.

Moreover, in this case, when forming the LDD structure of a transistor,it is preferable that the first high refractive index portion 3 has athickness equal to a gate electrode and film thickness direction, forexample, a thickness of approx. 200 nm. By using the thickness, it ispossible to simultaneously form the side wall of the LDD structure andfirst high refractive index portion 3 and decrease the number of manhours in addition to reduction of the number of damage on thephotoelectric conversion element 2. It is a matter of course that thenumber of man hours can be decreased because the samehigh-refractive-index film is used even when performing each etching inanother step. Moreover, it is possible to decrease the damage on aphotoelectric conversion element in the etching step even for thisthickness from FIG. 6.

In the case of any structure, it is possible to effectively use thefunction of an optical waveguide using the reflection on the interfacebetween a high refractive index portion having the above thickness andan insulating layer.

It is possible to use silicon oxide or silicon oxide doped withphosphorus, boron or fluorine as the material of the insulating layer 4covering the photoelectric conversion element 2 and first highrefractive index portion 3. It is also allowed that, for example, a gateinsulating film and gate electrode are present between the semiconductorsubstrate 1 and the insulating layer 4 though not illustrated.

In this case, “cross-section surface” is described by referring to FIGS.2A and 2B.

FIG. 2A shows the position of a cross-section surface horizontal to thelight receiving surface of the photoelectric conversion element 2 in thehigh-refractive-index portion. FIG. 2B is an illustrations obtained byprojecting the cross-section surface of the first high refractive indexportion 3 at the lines a-a′ and b-b′ in FIG. 2A. Moreover, in this case,symbol 2 in FIG. 2B shows the surface shape of the photoelectricconversion element 2 in FIG. 2A.

In this case, the cross-section surface at the line a-a′ is a firstcross-section surface of the first high-refractive-index portion 3. Thecross-section surface at the line b-b′ is a second cross-section surfaceformed at a position closer to the photoelectric conversion element thanthe first cross-section surface. It is allowed that position anddistance of these lines are changed when relative vertical relations areequal.

As previously described, in FIG. 2B, the area of the secondcross-section surface b-b′ of the first high-refractive-index portion 3is larger than the area of the first cross-section surface a-a′.

Moreover, in this case, it is preferable that the area of across-section surface at the lowest position of the firsthigh-refractive-index portion 3 is smaller than the surface area of thephotoelectric conversion element 2. That is, it is preferable that thearea of a cross-section surface facing the light receiving surface ofthe photoelectric conversion element 2 of a high-refractive-indexportion for forming an optical waveguide formed at a position closest tothe photoelectric conversion element 2 is smaller than the surface areaof the photoelectric conversion element 2. Thereby, it is possible todecrease the leak of light to a portion other than the photoelectricconversion element 2 and particularly, decrease of the leak of light iseffective when considering a shift during fabrication.

Then, the first pattern 5 is formed of a conductive material such asaluminum or copper. Moreover, the insulating layer 6 is formed of aninsulator, for example, silicon oxide.

The second pattern 7 is constituted of a conductive material such asaluminum or copper and may be formed as a light shielding film forlight-shielding the photoelectric conversion element 2 in addition towiring.

The second high-refractive-index portion 8 is formed directly on thephotoelectric conversion element 2 and contacts with the firsthigh-refractive-index portion 3. The second high-refractive-indexportion 8 is made of a transparent material for passing light and has arefractive index higher than that of the insulating layer 6. As thematerial satisfying the above condition, it is preferable to use aplasma SiN film, plasma SiON film, resist or titanium oxide. Moreover,it is allowed that the second high-refractive-index portion 8 serves asa passivation layer covering the second pattern 7.

Because the second high-refractive-index portion 8 contacts with thefirst high-refractive-index portion 3, light is not scattered and it ispossible to condense light to the photoelectric conversion element 2. Inthis case, it is more preferable that the second high refractive indexportion 8 is made of a material having the same refractive index as thatof the first high refractive index portion 3. This is becausereflections on these interfaces are able to be decreased. However, it isalso allowed that the same refractive index is not used. It is allowedto form an antireflection film on these interfaces in order to decreasereflections on the interfaces.

The planarized layer 9 is formed above the second high refractive indexportion 8 in accordance with necessity. Similarly, the color filterlayer 10 is also formed above the planarized layer 9 according tonecessity. The arrangement is a Beyer arrangement using three colors ofred, green and blue, for example. Moreover, the planarized layer 11 isformed above the color filter layer 10 according to necessity. Theon-chip microlens 12 is set above the planarized layer 11 to play a rolefor effectively taking in light into each pixel.

In this case, the relation between the refractive index of a materialfor forming an optical waveguide and the incident angle of light isshown below.

It is assumed that the refractive index of a high refractive indexportion in an optical waveguide is n1 and the refractive index of aninsulating layer at the outside of the area is n2. Then, when assumingthat the incident angle of the light incoming to the interface betweenthe high refractive index portion of an optical waveguide and aninsulating layer as θ a range for satisfying total reflection isθ>arcsin(n2/n1). In this case, the critical angle for total reflectionis assumed as θc=arcsin(n2/n1).

FIGS. 3A and 3B show vertical cross-section surfaces to the lightreceiving surface of the photoelectric conversion element 2 at anoptical waveguide portion.

First, a case is considered in which the interface between the highrefractive index portion of an optical waveguide and an insulating layeris vertical to the light receiving surface of a photoelectric conversionelement as shown in FIG. 3A.

The range in which the incident light C1 of an incident angle θ1total-reflects is θc<θ1<90°. However, when θ1 is smaller than θc, theincident light C1 is refracted without satisfying the total reflectioncondition on the interface between 3a and 4a. The refractive angle θ2 inthis case becomes θ2=arcsin(sin θ1*n1/n2). As a result, the incidentlight C1 does not contribute to photoelectric conversion but it becomescolor mixture or noise.

The first high refractive index portion 3 of this embodiment is formedso that the area of the second plane becomes larger than the area of thefirst cross-section surface. That is, as shown in FIG. 3B, the firsthigh refractive index portion 3 tilts toward the light receiving surfaceof the photoelectric conversion element at an angle of θ4.

When the incident light C1 enters FIG. 3B similarly to the case of FIG.3A, the incident angle for the interface between the high refractiveindex portion of an optical waveguide and an insulating layer becomesθ1+θ4. The incident angle of the incident light C1 satisfying the totalreflection condition is θc<θ1+θ4<90°. In this case, because the tiltangle θ4 is fixed, the range of the angle θ1 formed with the abovesemiconductor substrate to be changed by light becomes θc−θ4<θ1<90°−4.

That is, in the case of the optical-waveguide shape shown in FIG. 3B,total reflection is realized also when the incident light C1 moreobliquely enters compared to the shape in FIG. 3A. Therefore, byincluding the structure shown for this embodiment, it is possible tomake the incident light present in the above angular region efficientlyenter a photoelectric conversion element.

A fabrication method for forming the optical waveguide having the aboveshape is the same as the fabrication method to be described in detailfor a subsequent embodiment.

In this case, as previously described, it is preferable that the highrefractive index portion is present between 200 and 2,000 nm in the filmthickness direction. More preferably, the area has a thickness of 500 nmor more. It is possible to decrease the number of damage on aphotoelectric conversion element when forming the second high refractiveindex portion and a pattern is easily formed.

In FIG. 1 showing this embodiment, the highest portion of the first highrefractive index portion 3 and the lowest portion of the second highrefractive index portion 8 are illustrated as the same size. However, itis allowed to increase the dimension of either of them.

Moreover, in the case of this embodiment, a high refractive indexportion in which the area of the above-described second plane is formedso as to be larger than the area of the first cross-section surface isthe first high refractive index portion 3. In FIG. 3B, the lightreflected from the first high refractive index portion 3 enters in thedirection vertical to the photoelectric conversion element 2 by the tiltangle θ4 in the shape of the first high refractive index portion 3.Therefore, the condensing efficiency is improved. However, it is alsoallowed that the second high refractive index portion 8 has the shape.

Second Embodiment

FIG. 4 shows the photoelectric conversion device of this embodiment. Amember having the same function as the photoelectric conversion deviceof the above-described first embodiment is provided with the same symboland its description is omitted.

In this embodiment, the first cross-section surface of the second highrefractive index portion 8 is larger than the second plane of the area8, is therefore tapered. Thereby, it is possible to increase the lightentering an optical waveguide and improve the condensing efficiency of aphotoelectric conversion device.

In this case, “plane” is described below by referring to FIGS. 5A and 5Bsimilarly to the case of the first embodiment.

FIG. 5B is an illustration showing the plane of the second highrefractive index portion 8 at the line a-a′ and b-b′ in FIG. 5A byprojecting it from the upper portion. In this case, symbol 2 in FIG. 5Bshows the surface shape of the photoelectric conversion element 2 inFIG. 5A.

In this case, the plane at the line a-a′ is the first cross-sectionsurface of the second high refractive index portion 8. The plane at theline b-b′ is the second plane formed at a position closer to thephotoelectric conversion element than the first cross-section surface.In the case of positions of these lines, their distances may be changedas long as the cross-section surface at the line b-b′ is closer to thephotoelectric conversion element than the cross-section surface at theline a-a′. As previously described, in FIG. 5B, the first cross-sectionsurface a-a′ of the second high refractive index portion 8 is largerthan the second plane b-b′.

In this case, as described for the first embodiment, it is possible toreflect diagonal light depending on the shape of an optical waveguideformed by the high refractive index portion 3 and insulating layer 4.Therefore, in the case of the structure of this embodiment, the lightreflected from an optical waveguide formed by the high refractive indexportion 8 and insulating layer 6 is reflected to the light receivingportion of the photoelectric conversion element 2 in an opticalwaveguide formed by the high refractive index portion 3 and insulatinglayer 4 and the condensing efficiency is improved.

In the case of this embodiment, because the area of the firstcross-section surface of the uppermost layer high refractive indexportion 8 is larger than the area of the second plane, it is easy totake in incident light. Moreover, because the high refractive indexportion 3 is formed in which the area of the second plane is larger thanthe area of the first cross-section surface, it is possible toefficiently take in the light reflected from the previous structure.

Moreover, in this embodiment, though two optical waveguides are used, itis allowed to improve the condensing efficiency by providing theabove-describe function for an optional optical waveguide in three ormore optical waveguides.

Furthermore, the versatility of design of the first pattern 5 isimproved by forming the structure of this embodiment. Therefore, it iseasy to prevent the structure from being formed in the first highrefractive index portion 3 or second high refractive index portion 8,eclipse of light does not occur and it is possible to decrease colormixture and improve the condensing efficiency.

In FIG. 4 showing this embodiment, connective portions of the first highrefractive index portion 3 and second high refractive index portion 8are planes having an equal size. However, it is allowed to increase bothareas.

Third Embodiment

In this embodiment, a fabrication method of a photoelectric conversiondevice having an optical waveguide is described.

A well-shape structure for forming an optical waveguide can be formed inthe insulating layer by plasma etching. Specifically, an etching stoplayer which is hardly be etched rather than the insulating layer (theetch stop layer is, for example, silicon nitride layer) is formed on aphotoelectric conversion element to perform plasma etching up to aposition immediately above the photoelectric conversion element.

In this case, the plasma etching above the photoelectric conversionelement may increase the number of defects of the photoelectricconversion element and increase the dark current which is a noisecomponent of a sensor.

It is important to improve the S/N ratio which is the ratio between asignal (S) component and a noise (N) component in order to improve theperformance of a sensor. An optical waveguide has a configurationcapable of improving the condensing efficiency of incident light andincreasing the signal component. However, at the same time, the noisecomponent may be increased by the plasma etching. Particularly, in thecase of an amplifying-type photoelectric conversion device such as aCMOS sensor having many wiring layers, it is considered that the numberof damage is increased as a well-shaped portion increases in size.

The photoelectric conversion device fabrication method of thisembodiment is characterized by having a step of forming a highrefractive index portion serving as an optical waveguide on aphotoelectric conversion element and forming an insulating layer intowhich a high refractive index portion is fitted and then, forming apatterned layer. In general, a conductive layer such as wiring or lightshielding layer is used for a pattern. However, it is enough that adesired pattern is used without being restricted to the above case.

In this case, the high refractive index portion is formed on asemiconductor substrate correspondingly to a photoelectric conversionelement and the area and the element have a refractive index higher thanthat of an insulating layer constituting an optical waveguide.Specifically, they are formed of silicon nitride or oxynitridingsilicon.

Thus, by previously forming a high refractive index portion on aphotoelectric conversion element, it is not necessary to formwell-shaped portion immediately above a photoelectric conversion elementthrough plasma etching. That is, it is possible to reduce the increaseof dark current serving as a noise signal and improve the sensitivity byan optical waveguide. Even if a well-shaped portion is formed on theoptical waveguide, it is possible to decrease the damage by the plasmaetching on a photoelectric conversion element.

In this case, it is preferable that the high refractive index portionhas a thickness between 200 and 2,000 nm in the film thicknessdirection, preferably has a thickness of 500 nm or more. As shown inFIG. 6, it is possible to decrease the damage on a photoelectricconversion element by virtue of the high refractive index portion whenthere is an etching step after forming the high refractive indexportion.

Moreover, it is allowed that the high refractive index portion also hasa function of an etching stop layer.

Furthermore, when using a transistor having an LDD structure for aphotoelectric conversion device, it is possible to form the side wall ofthe transistor by using a high-refractive-index layer. A preferablethickness of the high-refractive-index layer is a thickness equal tothat of a gate electrode, for example, 200 nm. From FIG. 6, it is foundthat it is possible to decrease the number of damage on a photoelectricconversion element in the etching step even with this thickness.

Therefore, it is possible to effectively use the function of an opticalwaveguide using the reflection on the interface between a highrefractive index portion and an insulating layer at each thickness.

Moreover, by forming a high refractive index portion before a patternedlayer, it is possible to effectively use the light receiving surface ofa photoelectric conversion element and decrease the damage on thephotoelectric conversion element when forming the patterned layer.

In this case, the patterned layer denotes a wiring layer or lightshielding layer and is constituted of a conductive material such asaluminum or copper. However, a gate electrode made of polysilicon or thelike is not included. A pattern for specifying an opening of aphotoelectric conversion element is used to decide the outer peripheryof a region in which light enters a photoelectric conversion element. Byperforming optical simulation of the cross section of the element, apattern deciding the opening is known.

Specifically, a fabrication method is described below. FIG. 7 is aschematic sectional view vertical to a semiconductor substrate for onepixel of the previously-described CMOS-type photoelectric conversiondevice. In an actual photoelectric conversion device, a plurality ofpixels are formed on a semiconductor substrate.

The photoelectric conversion device of this embodiment has the followingconfiguration. In FIG. 7, the first high refractive index portion 3 andthe first insulating layer 4 are formed on the semiconductor substrate 1having the photodiode 2 serving as the photoelectric conversion element2. There are the first pattern 5 formed on the first insulating layer 4,second insulating layer 6 covering the first pattern 5 and secondpattern 7 formed on the layer 6. The second high refractive indexportion 8 is formed on the first high refractive index portion 3. Theplanarized layer 9 formed on the high refractive index portion 8, colorfilter layer 10, planarized layer 11 and on-chip microlens 12 arearranged in order.

The first high refractive index portion 3 is made of a transparentmaterial passing light and has a refractive index higher than that ofthe first insulating layer 4 present around the area. Specifically, itis preferable to use silicon nitride as the material of the highrefractive index portion 3.

This embodiment has a configuration in which the area of the secondplane at the photoelectric conversion element-2 side is larger than thearea of the first cross-section surface on which the first highrefractive index portion 3 is present. That is, the high refractiveindex portion is formed like a tapered shape. This shape can decreaseleak of light. Moreover, according to a conventional fabrication method,it is difficult to use a step of etching an insulating layer on thisshape and a step of embedding an optical refractive index material.However, it is possible to easily form this shape by the fabricationmethod of this embodiment. Of course, it is allowed that the interfacebetween the first high refractive index portion 3 and the insulatinglayer 4 is vertical to the light receiving surface of the photoelectricconversion element 2.

To form a tapered shape in which the area of the second plane of thefirst high refractive index portion 3 is larger than the area of thefirst cross-section surface, there is a control of conditions in dryetching. For example, anisotropic etching is performed by a plasmaetching apparatus by using gas such as CF₄, CHF₃, CH₂F₂, CO, O₂ or Ar.In this case, it is possible to realize a tapered shape by controllingvarious parameters such as gas flow rate, pressure, temperature, powerand inter-electrode distance.

The first insulating layer 4 covers the photoelectric conversion element2 and first high refractive index portion 3. It is preferable to use aninsulator having a refractive index lower than that of the first highrefractive index portion 3. Specifically, silicon oxide or silicon oxidedoped with phosphor, boron or fluorine is used. It is allowed to set,for example, a gate insulating layer and gate electrode between thesemiconductor substrate 1 and the first insulating layer 4 (notillustrated).

The first pattern 5 thereafter formed on the first insulating layer 4 isa wiring layer constituted of a conductive material such as aluminum orcopper.

It is enough that the second insulating layer 6 has a refractive indexlower than that of the first high refractive index portion 3.Specifically, it is preferable to use silicon oxide.

The second pattern 7 is constituted of a conductive material such asaluminum or copper, which may be formed as a light-shielding film forlight-shielding incident light incoming to the photoelectric conversionelement 2 in addition to the function of the wiring.

The second high refractive index portion 8 is formed on thephotoelectric conversion element 2 between the second patterns 7 bycontacting with the first high refractive index portion 3. The secondhigh refractive index portion 8 is made of a transparent materialthrough which light passes and a material having a refractive indexhigher than that of the first insulating layer 4 and second insulatinglayer 6. Specifically, it is preferable to use silicon nitride.

It is allowed that the second high refractive index portion 8 alsoserves as a passivation layer for covering the second pattern 7.Moreover, in this embodiment, the second high refractive index portion 8is formed into a shape in which the sectional area of the firstcross-section surface is larger than the sectional area of the secondplane. However, it is allowed that the interface between the second highrefractive index portion 8 and the insulating layer 6 is vertical to thelight receiving surface of the photoelectric conversion element 2.

The planarized layer 9 is formed above the second high refractive indexportion 8 according to necessity. The color filter layer 10 is formedabove the planarized layer 9 according to necessity to form three colorsof red, green and blue into Beyer arrangement. Moreover, the planarizedlayer 11 is formed above the color filter layer 10 according tonecessity.

Finally, the on-chip microlens 12 is formed above the planarized layer11 to play a role for effectively taking in light to the above highrefractive index portion.

FIGS. 8A, 8B and 8C show a fabrication flow for forming the first highrefractive index portion 3. First, a high refractive index material isformed like a layer on the semiconductor substrate 1 on which thephotoelectric conversion element 2 is formed. It is preferable to usesilicon nitride (refractive index n=2.0) obtained by using LPCVD orsilicon nitride (n=2.0) obtained by using plasma CVD. In this case, itis allowed to form a gate insulating layer and gate electrode beforeforming the first high refractive index portion 3.

Thereafter, the first high refractive index portion 3 is formed in adesired area by using a general semiconductor working technique. It ispreferable that the thickness of the high refractive index portion 3 is500 nm or more as previously described. Moreover, it is preferable thatthe upper limit of the thickness is equivalent to the bottom of thefirst pattern 5. Specifically, the upper limit is approx. 2,000 nm. Thisis because the first pattern 5 is easily formed.

Thus, by previously forming the high refractive index portion 3, it ispossible to decrease the number of damage on a photoelectric conversionelement compared to the case of a conventional fabrication method.Moreover, it is possible to decrease the number of damage on aphotodiode due to etching when forming the high refractive index portion8.

In this case, it is preferable that the area of a plane facing the lightreceiving surface of the photoelectric conversion element 2, that is,the area of the plane at the lowest portion of the first high refractiveindex portion 3 is smaller than the surface area of the photoelectricconversion element 2. This is because leak of light to a portion otherthan the photoelectric conversion element 2 is decreased andparticularly, this is effective when considering a shift duringfabrication.

Moreover, when forming the LDD structure of a transistor, it ispreferable that the first high refractive index portion 3 has athickness equal to that of a gate electrode in the film thicknessdirection, for example, approx. 200 nm. By using this thickness, it ispossible to form the side wall of the LDD structure and the first highrefractive index portion 3 at the same time and decrease the number ofman hours in addition to reduction of the number of damage on thephotoelectric conversion element 2. Because the same high refractiveindex layer is used even when performing etchings in separate steps, itis possible to decrease the number of man hours. Moreover, as shown inFIG. 6, it is possible to decrease the damage on a photoelectricconversion element in the etching step even with this thickness.

In the case of any structure, it is possible to effectively use thefunction of an optical waveguide using the reflection on the interfacebetween a high refractive index portion and an insulating layer at eachthickness.

Furthermore, in the case of a general process for first forming anetching stop layer among layers formed on a photoelectric conversionelement, an etching stop layer is left on an optical waveguide and aphotoelectric conversion element. Therefore, the function of the opticalwaveguide may be damaged. Moreover, it is considered to further applyetching to a portion corresponding to the optical waveguide of theetching stop layer. However, the photoelectric conversion element isdamaged by the etching step.

However, according to this embodiment, a high refractive index layer forconstituting an optical waveguide is first formed among layers formed ona photoelectric conversion element. Therefore, it is possible toconstitute an optical waveguide while decreasing the damage on thephotoelectric conversion element due to etching.

Moreover, as shown in FIG. 8C, the first insulating layer 4 is formed bycovering the first high refractive index portion 3. It is preferable touse a BPSG film obtained by doping silicon oxide with phosphor and boronfor the first insulating layer 4. After forming the first insulatinglayer 4, planarization such as CMP is performed according to necessity.

FIG. 8C shows a configuration for completely covering the upper portionof the first high refractive index portion 3 with the first insulatinglayer 4. This is because planarization is improved by forming theinsulating layer 4 on the whole surface when performing CMP. It is amatter of course to use a configuration in which the upper portion ofthe high refractive index portion 3 is peeled by performingplanarization such as CMP after forming the first insulating layer 4.

FIGS. 9D, 9E and 9F are illustrations showing a fabrication flow untilthe second high refractive index portion 8 is formed after forming thefirst high refractive index portion 3.

After forming the insulating layer 4, the first pattern 5 is formed. Itis preferable to use aluminum as the material of the first pattern 5.Moreover, it is allowed to use a copper pattern formed in accordancewith Damascene process. The same is also applied to the followingembodiment.

According to the sequence of steps of this embodiment, because the firsthigh refractive index portion 3 is previously formed, it is possible toform an optical waveguide by effectively using the area of the lightreceiving surface of the photoelectric conversion element 2. The designversatility of a high refractive index portion is improved and it ispossible to make the sectional area of the high refractive index portionthe maximum area for the surface area of photoelectric conversionelement. This becomes particularly effective when a pixel isminiaturized and the aspect ratio of a high refractive index portionrises.

Moreover, according to this step sequence, it is possible to protect aphotoelectric conversion element from the damage due to etching at thetime of patterning when a patterned layer is formed on a photoelectricconversion element.

Thereafter, the second insulating layer 6 and second pattern 7 areformed. As materials, the insulating layer 6 uses plasma silicon oxideand the pattern 7 uses aluminum.

FIGS. 10G, 10H and 10I are illustrations showing a fabrication flow forforming the second high refractive index portion 8.

After forming the second pattern 7, photoresist is formed and aphotoresist pattern 13 for forming the second high refractive indexportion 8 is formed by using the patterning technique. Then, the secondinsulating layer 6 and the first insulating layer 4 are etched throughplasma etching.

When the second insulating film 6 is plasma silicon oxide and the firstinsulating layer 4 is BPSG, plasma etching is performed by using CF gasrepresented by C₄F₈ or C₅F₈ and O₂ or Ar. In this case, by selecting anetching condition that, rather than the first high refractive indexportion 3, the second insulating film 6 and the first insulating layer 4are easily etched, it is possible to decrease the shaved quantity of thefirst high refractive index portion 3. Moreover, by selecting an etchingcondition, it is possible to perform etching like the tapered shapeshown in FIG. 10H. However, it is not always necessary to use thetapered shape.

Thereafter, by embedding a high-refractive-index material, the secondhigh refractive index portion 8 is formed. For example, silicon nitrideby high-density plasma CVD or high-refractive-index material by spincoat is embedded.

After embedding the high-refractive-index material, it is allowed toplanarize the upper portion by using resist etch back or CMP accordingto necessity.

In this case, it is preferable that the first high refractive indexportion 3 and the second high refractive index portion 8 are made ofmaterials having the same refractive index. This is because thereflection on the interface at their connective portion can bedecreased. However, it is not necessary that they are the same. In thiscase, it is also allowed to form an antireflection film for decreasingthe reflection on the interface on the interface.

In this embodiment, the second high refractive index portion 8 is formedby forming a well-shaped portion by etching. However, it is allowed topreviously pattern and form the second high refractive index portion 8similarly to the case of the first high refractive index portion 3.

As described above, according to a fabrication method of the presentinvention, it is possible to decrease the number of damage due to plasmaetching when forming an optical waveguide immediately above aphotoelectric conversion element. Therefore, it is possible to reducethe increase of the dark current which is the noise component of asensor.

Moreover, the same advantage is obtained from not only a high refractiveindex portion in which a plurality of optical waveguides are present butalso a configuration constituted of one area.

Fourth Embodiment

FIG. 11 shows a photoelectric conversion device of fourth embodiment. Amember same as that of the above-described third embodiment is providedwith the same symbol and its description is omitted. Moreover, thedescription on the same fabrication method is omitted.

The photoelectric conversion device of the fourth embodiment forms athird insulating layer 14 after forming the second pattern 7 toplanarize CMP or the like. Thereafter, the photoelectric conversiondevice performs well-shaped portion to form the second high refractiveindex portion 8. By planarizing the third insulating layer 14, it ispossible to stably perform the exposure in the etching step for formingthe second high refractive index portion 8.

In the case of this embodiment, by first forming the first highrefractive index portion 3 closest to the photoelectric conversiondevice 2, it is possible to reduce the increase of the noise componentdue to the damage by plasma etching. At the same time, by performingwell-shaped portion after planarizing an insulating layer, it ispossible to accurately perform the etching for making well-shapedportion and the condensing efficiency is improved.

Fifth Embodiment

FIG. 12 shows the photoelectric conversion device of this embodiment. Athird high refractive index portion 16 is formed in addition to thesecond high refractive index portion 8. Moreover, symbol 14 denotes athird insulating layer and 15 denotes a third wiring layer.

Furthermore, a member same as that of the first embodiment is providedwith the same symbol and its description is omitted and the descriptionon the same fabrication method is also omitted.

When forming an optical waveguide having a high aspect ratio formultilayer wiring, the aspect ratio for each layer is decreased byincreasing the number of layers and a high-refractive-index material iseasily embedded.

In the case of this embodiment, it is possible to reduce the increase ofthe number of noise components due to plasma damage by previouslyforming the first high refractive index portion 3 present at a positionclosest to the photoelectric conversion device 2 similarly to the caseof the first embodiment. Particularly, this is effective because aplurality of optical waveguides are formed. At the same time, by usingthree layers of high refractive index portions, it is possible to obtaina preferable embedding property also when forming an optical waveguidehaving a high aspect ratio by change of wiring layers to multilayer.

The shape of an optical waveguide is not restricted. Moreover, though aplurality of high refractive index portions are formed for eachembodiment, the advantage of even one area can be obtained according toa fabrication method of the present invention.

Application to Image-Pickup Module

FIG. 13 is a block diagram showing a case of applying a photoelectricconversion device fabricated by the fabrication method of aphotoelectric conversion device described in the first to fifthembodiments of the present invention to an image pickup module used fora portable unit.

There is a cover portion member 1104 for setting a photoelectricconversion device 1100 on a substrate 1107 made of ceramic or the likeand sealing the device 1100. The substrate 1107 is electricallyconnected with the photoelectric conversion device 1100. An opticalportion 1105 for taking in light and optical low-pass filter 1106 areset on the photoelectric conversion device 1100. Moreover, an imagepickup lens 1102 and a lens-barrel member 1101 for fixing the lens 1102,which cover the covering member 1104, are well sealed together with thesubstrate 1107.

In the case of this application, it is allowed that not only aphotoelectric conversion device of the present invention but also animage-pickup-signal processing circuit, A/D converter (analog/digitalconverter) and module control portion are mounted on the substrate 1107.Moreover, it is allowed that they are mounted on the same semiconductorsubstrate (1 in FIG. 1) with the photoelectric conversion device inaccordance with the same step.

Application to Digital Camera

FIG. 14 is a block diagram when applying a photoelectric conversiondevice fabricated by the photoelectric conversion-device fabricationmethod described in the first to fifth embodiments of the presentinvention to a digital camera serving as an image pickup system.

As an optical configuration for taking in light to a photoelectricconversion device 1204, there are a shutter 1201, image pickup lens 1202and aperture 1203. The shutter 1201 controls the exposure to aphotoelectric conversion device 1204 and incident light is imaged on thephotoelectric conversion device 1204 by the image pickup lens 1202. Inthis case, light quantity is controlled by the aperture 1203.

A signal output from the photoelectric conversion device 1204 inaccordance with taken-in light is processed by a signal processingcircuit 1205 and converted from an analog signal to a digital signal byan A/D converter 1206. The output digital signal is computed by a signalprocessing portion 1207 and image pickup data is generated. The imagepickup data can be accumulated in a memory 1210 mounted on a digitalcamera or transmitted to an external unit such as a computer or printerthrough an external I/F portion 1213 in accordance with operation modesset by a user. Moreover, it is possible to record the image pickup datain a recording medium 1212 which can be set to or removed from a digitalcamera through a recording-medium control I/F portion 1211.

The photoelectric conversion device 1204, signal processing circuit1205, A/D converter 1206 and signal processing portion 1207 arecontrolled by a timing generating portion 1208 and the whole system iscontrolled by a general-control and computing portion 1209. It ispossible that these systems are formed on the same semiconductorsubstrate (1 in FIG. 1) as the photoelectric conversion device 1204 inthe same step.

This application claims priority from Japanese Patent Application Nos.2005-280108 filed on Sep. 27, 2005 and 2005-280109 filed on Sep. 27,2005, which are hereby incorporated by reference herein.

The invention claimed is:
 1. A method of fabricating a photoelectricconversion device, comprising the steps of: forming on a substrate afilm covering a photoelectric conversion element and a gate electrode ofa transistor; forming a first portion on at least a part of a lightreceiving surface of the photoelectric conversion element, and a sidewall on the gate electrode for a lightly doped drain (LDD) structure ofthe transistor, wherein the first portion and the side wall are formedfrom the film by etching the film; forming on the substrate a firstinsulating layer that covers the first portion; forming a copper patternon the substrate after forming the first insulating layer; forming onthe substrate a second insulating layer that covers the first portionand the copper pattern; forming a well-shaped portion by etching thesecond and first insulating layers, said first portion being positionedbetween the light receiving surface and the well-shaped portion in adirection vertical to the light receiving surface; forming a secondportion by embedding a transparent material in the well-shaped portion,said first portion being positioned between the light receiving surfaceand the second portion in the direction vertical to the light receivingsurface, and said first and second insulating layers being presentaround the second portion in a direction horizontal to the lightreceiving surface.
 2. The method according to claim 1, comprisingforming a plurality of first portions corresponding to a plurality ofthe photoelectric conversion elements.
 3. The method according to claim1, wherein a refractive index of the second portion is different from arefractive index of the first portion, and a film is positioned betweenthe first portion and the second portion.
 4. The method according toclaim 1, wherein the second portion is formed in contact with the firstportion.
 5. The method according to claim 1, wherein a distance from thelight receiving surface to a bottom of the well-shaped portion is 200 nmto 2000 nm.
 6. The method according to claim 1, further comprisingplanarizing the first insulating layer.
 7. The method according to claim1, further comprising forming a conductive pattern on the substrateafter forming the second insulating layer and before forming thewell-shaped portion.
 8. The method according to claim 1, wherein thefirst insulating layer is formed around the first portion in a firstplane and a second plane, the first and second planes being along thedirection horizontal to the light receiving surface, and the secondplane being between the first plane and the light receiving surface, across-sectional area of the first portion in the first plane beingsmaller than a cross-sectional area of the first portion in the secondplane.
 9. The method according to claim 1, wherein the second insulatinglayer is formed around the second portion in a third plane and a fourthplane, the third and fourth planes being along the direction horizontalto the light receiving surface, and the fourth plane being between thethird plane and the light receiving surface, a cross-sectional area ofthe second portion in the third plane being larger than across-sectional area of the second portion in the fourth plane.
 10. Themethod according to claim 1, wherein the second portion is formed incontact with the first portion and the cross-sectional area of thesecond portion in the third plane is larger than a contact area betweenthe first portion and the second portion.
 11. The method according toclaim 1, wherein the first portion comprises silicon nitride oroxynitrided silicon.
 12. The method according to claim 1, wherein thetransparent material comprises silicon nitride.
 13. The method accordingto claim 1, wherein the first portion and the second portion comprisessilicon nitride.
 14. The method according to claim 1, wherein theetching of the first and second insulating layers is performed by plasmaetching.
 15. The method according to claim 1, wherein the transparentmaterial is embedded by high-density plasma CVD or spin coat.
 16. Themethod according to claim 1, wherein the first insulating layercomprises silicon oxide or silicon oxide doped with at least one ofphosphorus, boron or fluorine.
 17. The method according to claim 1,further comprising forming a microlens above the second portion, whereinthe transparent material embedded in the well-shape portion does notexist between an upper face of the second insulating layer and themicrolens in the direction vertical to the light receiving surface. 18.The method according to claim 7, further comprising forming a thirdportion including a first part and a second part, the conductive patternbeing positioned between the second insulating layer and the first part,and the second portion being positioned between the second part and thefirst portion, wherein a distance between the second part and thesubstrate is smaller than a distance between the first part and thesubstrate.
 19. An image pickup module comprising the photoelectricconversion device fabricated by the method according to claim 1, a lensmember for imaging light on the photoelectric conversion device, and alens-barrel member for holding the lens member.
 20. An image pickupsystem comprising the photoelectric conversion device fabricated by themethod according to claim 1, and a signal processing circuit forprocessing a signal output from the photoelectric conversion device.